Lightpoints are small sources of light such as stars, beacons, and runway lights. Depicting lightpoints in a realistic manner is an important part of making three-dimensional images believable. Realistic depiction of lightpoints is difficult, however, when the intended application is a simulation environment, such as a flight simulator or virtual reality environment. This difficulty is caused by the need to constantly adjust the appearance of lightpoints as they shift in relation to the viewer's eye.
As an example, consider the case of a flight simulator depicting a nighttime approach to a runway. Typical runways are surrounded by runway lights. For the flight simulator, each of these runway lights is a lightpoint. These lightpoints must be rendered in a realistic fashion from the point where they first become visible to the point where the runway is beneath the plane. Clearly, this involves a great change in perspective. For the simulation to be believable, the runway lights must have a realistic appearance over this entire perspective change.
Traditionally, lightpoints have been rendered as collections of raster pixels. The collections of pixels produce a fixed size image that does not change To account for changes in perspective. As a result, lightpoints that appear to be correctly sized when viewed from a distance will appear to shrink (in relation to background images) as they are approached. Rendering light points as collections of raster pixels also tends to produce aliasing within the pixels of the lightpoints. Aliasing results because lightpoints typically have a round or elliptical cross-section. This cross-section must be mapped to square pixels. As a result, edges of the cross-section may fall between adjacent pixels and need to contribute partially to both pixels. The fixed size and aliasing produced by rendered lightpoints as collections of raster pixels compromises the realism of this technique.
An alternative is to render lightpoints as calligraphic images. The calligraphic images are overlaid onto a background image produced using normal raster techniques. Use of calligraphically rendered lightpoints eliminates the aliasing present in lightpoints created using raster techniques. Unfortunately, calligraphic rendering requires specialized hardware. As a result, the use of calligraphic techniques may be impractical for many simulation environments.
Thus, a need exists for a high performance method for rendering lightpoints that avoids or reduces lightpoint shrinking and pixel aliasing. This need is especially important for simulation environments, such as flight simulators and for highly realistic virtual reality systems.